Colorimetric method for the determination of captafol (difolatan) in commercial formulations and residues on grains and apples.

A simple and rapid colorimetric method for the microdetermination of captafol (difolatan), based on its reaction with a dithiocarbamate, has been developed. The bright yellow colour which develops instantaneously on mixing the fungicide with the reagent is stable for at least 12 h. The method has been successfully adapted to the determination of captafol in its formulated products and residues on grains and apples.     

Spectrophotometric determination of ziram, ferbam and zineb with diphenylcarbazone

A procedure has been developed for the determination of ziram (zinc dimethyldithiocarbamate), ferbam (ferric dimethyldithiocarbamate) and zineb (zinc ethylenebisdithiocarbamate) after their decomposition and extraction of the diphenylcarbazone complexes of the zinc or iron into isobutyl methyl ketone. These complexes absorb strongly at 520 nm. The method is rapid, sensitive and selective and can be used for the determination of these dithiocarbamates in commercial and synthetic mixtures.     

Analytical application of embelin

Summary Embelin is employed as a reagent for the gravimetric individual estimation of alkaline earth metals and magnesium.

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Zusammenfassung Zur gravimetrischen Einzelbestimmung von Magnesium und den Erdalkalien wird Embelin als Reagens empfohlen.

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Part III: Z. analyt. Chem. 185, 216 (1962).     

Analytical applications of the photochemical action of light: Determination of oxalic acid by photo-oxidation in the presence of ferric salts

A new method has been developed for the determination of oxalic acid. This depends upon the photochemical oxidation of oxalic acid in. the presence of ferric sulphate. The method involves exposing a measured volume of oxalic acid solution, with an excess of ferric alum and some sulphuric acid,tosunlight in quartz or pyrex beaker for 15 to 30 minutes. The progress of the reaction is indicated by the disappearance of the yellow colour of the ferricoxalate complex from the solution. After completion of the reaction, the ferrous salt formed is determined using standard sodium vanadate and either diphenylbenXXXdine or diphenylamme-sulphonate as internal indicator in the presence of sufficient phosphoric acid. Formic acid does not interfere in the photochemical method of deteminination.     

Potentiometric titration of permanganate with resacetophenone oxime

Milligram amounts of permanganate can be titrated with resacetophenone oxime (4-acetylresorcinol oxime) as a reducing titrant in the presence of phosphoric acid (0.5 M). The stoichiometry between permanganate and the oxime is 3:1 (MnO₄^-:oxime). The titration is successful in the presence of large amounts of dichromate or vanadate or moderate amounts of cerium(IV).     

Photoelectron spectra of substituted benzenes

Photoelectron spectra of several substituted dimethylanilines, nitrobenzenes, acetophenones and nitrosobenzenes have been studied with a view to examine the electronic effects of substituents on the various φ and n levels. The results are discussed in the light of molecular orbital calculations and electronic absorption spectra. Correlation of substituent effects on the IE's with π-electron densities and Hammett substituent constants has enabled rationalization of all available data on mono- and disubstituted benzenes. The IE's generally increase with the electron-withdrawing power of the substituents.     

Comparison of standards in the Karl Fischer method for water determination.

The use of 4-(5-nonyl)pyridine oxide and trioctylamine oxide for the extraction of niobium(V) from different mineral acid solutions is described. The influence of the concentration of the solvents, acids and salting-out agents is discussed. Separations of niobium(V) from tantalum(V) and zirconium(IV) have been achieved.     

Cyclization by the intermediates of phenylthio- and phenoxy carbamoyl. Formation of azasuccinic anhydrides and their polycondensation products. Intervention of the carbamoyl pyridinium cation

The N-(p-nitrophenoxy-carbonyl) derivatives of glycine, DL -alanine and DL -leucine are transformed by the action of pyridine into azasuccinic, 3-methyl-2-azasuccinic and 3-isobutyl-2-azasuccinic anhydride, respectively. These cyclisations occur probably via the intermediate N-carbamoyl-pyridinium cation , the rate of cyclisation seems to depend on the concentration of the intermediate in the form of the dipolar ion , i.e. the ionised carboxyl is necessary for the reaction. In γ-collidine the cyclisation occurs very slowly; this is attributed to the slowness due to steric hindrance of the production of N-carbamoyl-γ-collidinium cation and its instability. The azasuccinic anhydrides mentioned polycondense, yielding the corresponding polyglycine, poly-DL -alanine and poly-DL -leucine. This reaction too is catalysed by pyridine; it can also be effected by γ-collidine, but the efficacity of the latter in comparison with pyridine is even less than in the catalysis of the cyclisation described above. N-(p-nitrophenoxy-carbonyl)-glycine reacts with lysozyme in the presence of pyridine; several glycine residues are introduced into the enzyme molecule, the product being insoluble and poorly active.     

Stereospecific reactions of copper(II) complexes of serine and threonine with formaldehyde

Summary Condensations of Cu(L-ser)₂ and Cu(L-thr)₂ (where L-ser=L-serinato anion and L-thr=L-threoninato anion) with formaldehyde at pH 4.5 yield two new optically active products:bis[L-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) andbis[L-(N-hydroxymethyl-5-methyloxazolidine-4-carboxylato)]copper(II) dihydrate (2), respectively. Cu(D-ser)₂ and Cu(D-thr)₂ also undergo similar reactions. The new products are different from the products obtained from Cu(DL-ser)₂ and Cu(DL-thr)₂, and a mechanism has been suggested to explain the stereospecificity of these conversions. Condensation of Cu(L-ser)₂ with formaldehyde and ammonia at pH 4.5 yields the new product, [3N,7N-(1,3,5,7-tetraazabicyclo-[3.3.1]nonyl)di(hydroxymethyl)-acetato]copper(II), (3). The compexes have been characterized by analytical and by i.r. electronic and c.d. spectral data. Complexes (1) and (2) undergo a reversible Cu^II/Cu^I redox process in aqueous media at –0.18 Vversus s.c.e.; complex (3) exhibits irreversible Cu^II/Cu^I reduction at –0.49 V confirming the presence of a rigid pentamethylenediaza-bridged ligand system.     

Gas Hydrate Formation in Reversed Micelles

We describe a technique to modify protein solubility and optimize enzyme activity in reversed micellar solutions. The technique is based on the ability of hydrates of natural gas to form in the micro-aqueous phase. Clathrate hydrates are crystalline inclusions of water and gas, and their formation in bulk water has traditionally been studied with relevance to natural gas recovery. We have found that hydrates can form in the environment of the microaqueous pools of reversed micelles, and that their extent of formation can be well controlled through the thermodynamic variables of temperature and pressure. Additionally, formation of hydrates affects the size and aggregation number of the micelles, and thus influences the solubility and conformation of encapsulated proteins. We demonstrate how the concept can be used in two applications: (i) protein extraction into reversed micelles and subsequent recovery, and (ii) optimization of enzyme activity in reversed micelles.